Many types of input devices are presently available for performing operations in a computing system, such as buttons or keys, mice, trackballs, touch sensor panels, joysticks, touch screens and the like. Touch screens, in particular, are becoming increasingly popular because of their ease and versatility of operation as well as their declining price. Touch screens can include a touch sensor panel, which can be a clear panel with a touch-sensitive surface, and a display device that can be positioned behind the panel so that the touch-sensitive surface can substantially cover the viewable area of the display device. Touch screens can allow a user to perform various functions by touching the touch sensor panel using one or more fingers, a stylus or other object at a location dictated by a user interface (UI) being displayed by the display device. In general, touch screens can recognize a touch event and the position of the touch event on the touch sensor panel, and the computing system can then interpret the touch event in accordance with the display appearing at the time of the touch event, and thereafter can perform one or more actions based on the touch event.
Touch sensor panels can be formed from a plurality of drive lines and sense lines, with sensors or pixels present where the drive and sense lines intersect each other. The drive lines can be simultaneously stimulated by low-voltage stimulation signals and touch events can be detected because the charge injected into the sense lines due to the applied stimulation signals is proportional to the amount of touch. Many sources of noise can interfere with the sense lines' outputs, making it difficult to detect the outputs and hence identify touch events. The low supply voltages for the stimulation signals can reduce both the power requirements and the sizes of the touch screens. However, the low supply voltages increase the difficulty in detecting the sense lines' outputs over the noise.